Three sets of studies in the field of developmental pathology are being prosecuted under this grant. These are: 1. An investigation of chromosomal aberrations and their inheritance and etiology in man and animals. These studies include studies of mentally retarded patients and of a "cancer" family. The chromosome morphology of several animals is being investigated. 2. An analysis of fibrillar-neuronal organization in the cerebral cortex of fetuses, neonates and young infants, to establish thereby "normal" patterns of intracortical organization and against which aberrations of cortical development can be compared. With these baselines established in normals, a study of the brains of mentally retarded individuals has been initiated. 3. A study of virus-cell-host interactions operative in infections of fetal and suckling animals, seeking to establish experimental models elucidating the role of viruses in the pathogenesis of reproductive failure and disorders of development in man.